Reporter: They are those among us with the least. Almost half a million people who call the streets home. Their meals, whatever they can find. Whatever they are given. Help me out, get something to eat? Reporter: "What would you do?" If you saw a good samaritan give a homeless man $20 for a bite to eat -- get whatever you want, okay? Reporter: Only to see him tossed back to the curb the second she leaves. Just, it's bad for business. I can't let you sit in here. Reporter: A man denied service simply because he's homeless. Today, we brought our hidden cameras to the streets of lynnbrook, new york, and McQUAID'S RESTAURANT. Of course, both traci and kevin are actors and the bartender, jeremy -- not your money. Get out of here. Reporter: He's definitely an actor. Everyone at this bar knows except this man and our hidden cameras are rolling. Oh, wow, it's nice in here. Hi. This is a friend of mine. You have a menu or something he can look at. Get whatever you want, okay? Here's $20. Really, really nice. Reporter: Right away, he takes notice. Take care, okay? Thank you so much. I have to get back to work. Reporter: As soon astray si leaves, jeremy has a change of heart. Listen, there are places you can go, a soup kitchen or something. I'm a paying customer. I got $20. That's not your money. I don't want you to bother -- I'm not bothering -- Reporter: This is about more than just manners. You took his $20. Not his $20. His $20. She gave it to him. For him to eat. I heard it. Okay, if I give this 20 back to him, what is he going to do. Whatever he wants. Reporter: He's going to go buy liquor. He wanted to eat. That's what he's looking for. Reporter: We've barely begun here. But already, a bold move. Who are you calling? Police. On me? Yeah. Reporter: He makes it clear to jeremy it's meal or no deal. Give him back the 20. Thank you. Reporter: Not everyone is quite so welcoming. Uh-oh. Got a homeless guy outside. Reporter: But now the homeless guy is inside. You have a menu that I can look at? Reporter: These two women don't want a homeless man seated anywhere near them. These ladies and I can smell you, too, you smell. Reporter: And when jeremy intervenes, they offer an alternative. Bothering you, right? Well, let him take something to go to eat. But he shouldn't sit here, right? No. No. I'll be outside, okayr? Sorry about that, ladies. No problem. I wouldn't have cared if he smelled. Hope that didn't ruin your appetite. Well, it didn't help. Reporter: Tough day for kevin. These next two men also give him the cold shoulder. Am I bothering you guys? I'm just trying to get something to eat. These guys work, right? They work all their lives and they pay for their food. Reporter: They won't even look our homeless man in the face. Excuse me. We're not getting involved here. Can't. We don't own the place. Imagine you are down on your luck. Help a guy out. Sir. Mind your own business. Repr: With his pleas falling on deaf ears, we tell kevin to leave. Sorry, guys. You feed them once, you feed them twice and there's 20 guys sitting here. Absolutely. Reporter: They agree with jeremy. Why? Think it was wrong for a lady to walk in here bring a homeless guy in here. If that's her friend, take the money and buy a sandwich somewhere. Reporter: But not here? Wrong place. Reporter: Wrong place. And, as this next man walks in, things only get worse. Run him through the dishwasher in the back. Yeah. I just want to get food. Don't cough on everything. Reporter: Among with jeremy, he literally laughs at kevin's misfortune. Can I please get a sandwich? No. Oh, my god. Give the guy a couple of croutons from the floor of the kitchen or something. I'm a paying customer, man. Here's the thing. I don't work in a soup kitchen. I work in a bar, okay? Reporter: It seems like he couldn't care less about our homeless man. But then he realizes there's more at stake here. Can you give me my money back? Confiscated his money? I'm not -- give the guy -- you have to give him his money back. Going to buy booze with this? No. Reporter: Now watch what happens when kevin leaves the restaurant. I just don't think homeless people should be allowed in bars, you know? How did he end up here? He wasted his money. Well, we don't know that. We don't know that. That's true. I mean -- looks like a decent guy. Reporter: A decent guy. And as it turns out, so is anthony gambino. Do me a favor, make the guy a sandwich and put it on my bill, okay. Make him -- make him a sandwich. Kevin, this guy said he wants to buy you a sandwich. You're kidding me, that guy? What kind of sandwich? Turkey burger. He need as little something more than that. More than that? That's for weight watchers. Get him the -- the short skirt steak tacos. A lot of protein in that. 100%. Reporter: And now, anthony, a man who seconds ago was insulting kevin hand delivers his meal. You hungry? Here you go, pal. Serious? Yeah. Thank you. Your welcome. Enjoy. You want a beer or something. Reporter: Before he buys him a round of drinks, time to introduce ourselves. . Reporter: Started off joking with the guy -- yeah, trying to rile him up a little bit on his first day. Reporter: And then you did something that totally surprised us. I've had some hard times in my life and other people were there for me, so, I try to do the same thing. Reporter: Paying it forward. This next man understands that concept all too well. As soon as he sees kevin on the street. Thanks, bud. Can you just sit right here? Reporter: Seconds later, kevin is seated right next to him. I don't want you bo bother -- he's not bothering me. Why don't you have some soup? You've never been there. You don't know what it's like. Well, I work, you know? Yeah, we all work. But all of us have had bad times. Can I get, like, a glass of water, just water? Reporter: A small request that leads to a touching moment. Thank you. Now you're making him give you his drink? No. Don't worry about it. Thank you. You're welcome. To your health. To yours, too. Thank you. Better times. Reporter: But from jeremy, the insults just keep getting worse. There's a hose out there somewhere. You don't have to be cruel, man. You want me to be cruel? Get out of here. I hope you enjoyed your water. Why did you take the money, buddy? You know what he's going to do? He's going to buy drugs and alcohol. He may. But you can't take that money from him. You take that money from him, you're stealing and I'm going to make sure you getested for it. Why are you defending a homeless guy? Because you're a prick. Reporter: Kevin leaves. Sorry if that upset you. I hope I did the right thing. No, you didn't. . Reporter: And arnie gerber is full of emotion. Think I was wrong? Absolutely. Completely wrong. Really? You've never been in bad shape? You've never needed help? You never had anything happen to you that you wish didn't or that you wish you could get out of? We don't know what the hell happened to this poor guy. Reporter: It's a message that's very personal to arnie. And you said to him, haven't you ever been through hard times? Haven't we all? Everybody's been through hard times. And we survive them in some way. And if somebody helps you and gives you a push up, fine. Reporter: Almost half of the people we met this day did just that. They spoke up for a hungry stranger down on his luck. Heroes, they don't think so. Heroic is the guy that landed the plane in the hudson river. That's heroic. Wouldn't anybody else do the same thing?

This transcript has been automatically generated and may not be 100% accurate.

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